The present invention relates to a device for contactless gripping, holding, and positioning of preferably contact-sensitive components.
In case of contact-sensitive components, e.g. wafers, particles axe removed at contact points during mechanical contact, which may negatively influence a technological working process depending on the pre-determined conditions of the edges.
To avoid particle degeneration or damage to the surface of a component, non-contact gripping devices have been developed that use overpressure and/or partial. vacuum of flowing gases to hold the component as described in Goodwin et al. U.S. Pat. No. 5,080,549. This type of gripper will be termed as pneumatic gripper in the following.
However, it is of significance during transporting of wafers in clean rooms that the technologically required airflow (laminar flow condition) is not negatively influenced in these clean rooms. The air flowing in or out of jets of the gripper disturbs the laminar flow condition in the clean room and increases thereby the risk of freely-traveling particles influencing the quality of manufacturing.
An additional disadvantage of blowing grippers is the high vorticity of the air discharging from the jets. Particles that axe stuck to the underside of the wafers, for example, may thereby freely travel and deposit themselves on the top surface of the wafer as well.
It is the object of the invention to provide a technology that avoids the disadvantages of the pneumatic gripper mentioned above.
The invention is a contactless gripping and holding device provided is for components whose gripping and holding forces axe produced according to the principle of acoustic standing wave levitation, The peculiarity of this gripping and holding device exists in the fact that only the edge sections of the components protrude into the acoustic field of force pattern and are held in place there by Bernoulli forces. Thus, then total area of the sound-radiating surfaces of the sound-producing means may be considerably smaller than the top surface area of the component being levitated, i.e., smaller than the component""s total surface area facing the sound-producing means.
In contrast, the sound-radiating surfaces in the traditional acoustic standing wave levitation define a total surface area that is considerably larger than the top surface of the levitated item.
In one aspect of the invention, it is assumed that the edge sections of the component protruding into the acoustic field of force are designed in such a manner that they act as reflectors, which means that a reflector, which is always necessary in the traditional acoustic standing wave levitation, is no longer required.
It must be especially mentioned that not only completely flat items, as wafers for example, may be held. Only the edge surfaces or some sections of these edge surfaces must have the required reflection characteristics, which means, they must reflect the striking sound wave again in the direction of the source of sound. It must be mentioned as well that the edge surfaces acting as reflector may lie also within the component""s surface should the component be provided with a boring or other openings, for example.
The device can be supplemented with separate reflectors, which increase the holding forces. This type of arrangement is provided when the edge sections of the item have rather poor reflection characteristics.
The spatial position and/or the geometric shape of the sound-producing means and of the reflectors are selected depending on the shape of the component being levitated. Only similar shaped components may therefore be held, which is, however, also often times a characteristic for traditional gripping and holding devices.
Additional sound sources could be employed in place of reflectors whereby the holding forces of the gripper may be additionally increased. Those skilled in the art know that the respective sound sources, which are emitting sound against each other, must be tuned to one another to adjust the energy nodal at one plane.
In conclusion, it must be mentioned that the gripping devices according to the present invention may be employed especially advantageously in technological processes in which the operational steps of horizontal and vertical transporting as well as storing or interim storing occur according to the principle of acoustic levitation or according to the principle of sound pressure in the vicinity of the source of sound. Such a system operates also reliably without gravitation.